Hi everybody
I'm working on a Stevens 520? 12 ga.
The action was locked open after some abuse.(not me)
I took it apart and got things working again, but now the action won't unlock after the trigger is pulled.
I've had it apart several times looking at everything I can think of, but I don't see anything in the action that unlocks the bolt after fireing. I still have to push the button on the bottom to let the slide come back.

Was this gun made that way? Or am I missing something?
Any suggestions would be appreciated.

It's one of John M Browning's tricks. It's an Inertia activated lock.
It will unlock just fine in live fire but won't when dry fired.
So the correct operation when dry firing is to push forward on the slide that will unlock the bolt and allow you to operate it as normal.

Excellent, thanks much

A few early production 520's do have an inertia lock in the action (in the trigger group assembly) If you take it apart again, it's a counter weight approx 1/2" sq and is located on the left side just forward of the trigger. It comes out with the trigger guard assembly.


Those shotguns will not open when dry fired (or a dud round in the field) w/o using the slide release to open the action.
No recoil,,the gun can't be opened w/o manually using the slide release latch.

This was a early design in the 520 and did not last too long. I suspect it was included because of the suspected unreliable nature (hang fire) of shotshells and to avoid one being ejected and going off with the breech unlocked at that point.

Marlin hammerless pump shotguns (Mod 43, 53, etc) all have the same feature and kept it through their mfg lifetime.

In normal operation when the trigger is pulled,,and other models of the 520 that don't have the inerta block in the action (most all of them!), the action will operate with no extra motion needed to the action slide other than a pull it to the rear motion.

I've had at least 15 different Mod 520 and 520A shotguns and still shoot 2 of them regularly at skeet.